That bad old M106

I’ll post a few thoughts here about restoring a neglected M106. This one seems to has a solid basis for a build, but although the hardware is lovely, actual condition remains to be seen.

If you’re not sure what an M106 is, it’s really just a factory-modified turbocharged M30. The motor was never offered in the US, but many found there way here via the gray market. These motors were only used in the mid-80s European-specification 745i sedan. They also were only offered with automatic transmissions (unless you knew someone important in Munich, I’d guess). Considering how rare these cars are, I’ve been fortunate enough to already have owned one: I rescued an ’84 745i from an abandoned vehicle impound a while back.

The M30 is a pretty overbuilt engine, so there really aren’t a lot of M106-specific differences. Lower-compression pistons with piston-cooling oil jets, different exhaust manifold, air-to-air intercooler, KKK K27 turbo and wastegate, integrated DME (with integrated automatic transmission TCU and Bosch knock sensor computer). A few powertrain upgrades like a large-case diff and higher-capacity radiator pretty much completes the list.

The aftermarket took to these engines pretty early, and you can see builds using this engine on many enthusiast sites. There were more than a few other turbocharger kits built for the M30. Calloway even offered one for years.

This specific car was apparently a normal US-market 735i 5-speed. The M106 was spliced into the car but it’s still run by a modified M30 DME & wiring harness. A chip from TCD tuning tweaks the ignition timing to prevent knocking, and a rising-rate fuel pressure regulator handles the fueling.